<template>
    <canvas id="cas"></canvas>
</template>
<script>
    export default{
        props:{
            color:{
                type:String,
                default:'red'
            },
            bgcolor:{
                type:String,
                default:'rgba(0,0,0)'
            },
            width:{
                type:String,
                default:"500"
            },
            height:{
                type:String,
                default:"500"
            }
        },
        data(){
            return{

            }
        },
        methods:{
            animate:function(){
                var _this=this;
                var canvas = document.getElementById("cas");
                canvas.style.background=_this.bgcolor;
                var ctx = canvas.getContext("2d");

                resize();
                window.onresize = resize;

                function resize() {
                    canvas.width = _this.width;
                    canvas.height = _this.height;
                }

                var RAF = (function() {
                    return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame || function(callback) {
                        window.setTimeout(callback, 1000 / 60);
                        };
                })();

                // 鼠标活动时，获取鼠标坐标
                var warea = {x: null, y: null, max: 20000};
                canvas.onmousemove = function(e) {
                    e = e || window.event;
                    warea.x = e.clientX;
                    warea.y = e.clientY;
                };
                canvas.onmouseout = function(e) {
                    warea.x = null;
                    warea.y = null;
                };

                // 添加粒子
                // x，y为粒子坐标，xa, ya为粒子xy轴加速度，max为连线的最大距离
                var dots = [];
                for (var i = 0; i < 300; i++) {
                    var x = Math.random() * canvas.width;
                    var y = Math.random() * canvas.height;
                    var xa = Math.random() * 2 - 1;
                    var ya = Math.random() * 2 - 1;

                    dots.push({
                    x: x,
                    y: y,
                    xa: xa,
                    ya: ya,
                    max: 6000
                    })
                }

                // 延迟100秒开始执行动画，如果立即执行有时位置计算会出错
                setTimeout(function() {
                    animate();
                }, 100);

                // 每一帧循环的逻辑
                function animate() {
                    ctx.clearRect(0, 0, canvas.width, canvas.height);

                    // 将鼠标坐标添加进去，产生一个用于比对距离的点数组
                    var ndots = [warea].concat(dots);

                    dots.forEach(function(dot) {

                    // 粒子位移
                    dot.x += dot.xa;
                    dot.y += dot.ya;

                    // 遇到边界将加速度反向
                    dot.xa *= (dot.x > canvas.width || dot.x < 0) ? -1 : 1;
                    dot.ya *= (dot.y > canvas.height || dot.y < 0) ? -1 : 1;

                    // 绘制点
                    ctx.fillRect(dot.x - 0.5, dot.y - 0.5, 1, 1);

                    // 循环比对粒子间的距离
                    for (var i = 0; i < ndots.length; i++) {
                        var d2 = ndots[i];

                        if (dot === d2 || d2.x === null || d2.y === null) continue;

                        var xc = dot.x - d2.x;
                        var yc = dot.y - d2.y;

                        // 两个粒子之间的距离
                        var dis = xc * xc + yc * yc;

                        // 距离比
                        var ratio;

                        // 如果两个粒子之间的距离小于粒子对象的max值，则在两个粒子间画线
                        if (dis < d2.max) {

                        // 如果是鼠标，则让粒子向鼠标的位置移动
                        if (d2 === warea && dis > (d2.max / 2)) {
                            dot.x -= xc * 0.03;
                            dot.y -= yc * 0.03;
                        }

                        // 计算距离比
                        ratio = (d2.max - dis) / d2.max;

                        // 画线
                        ctx.beginPath();
                        ctx.lineWidth = ratio / 2;
                        ctx.strokeStyle = _this.color;
                        ctx.moveTo(dot.x, dot.y);
                        ctx.lineTo(d2.x, d2.y);
                        ctx.stroke();
                        }
                    }

                    // 将已经计算过的粒子从数组中删除
                    ndots.splice(ndots.indexOf(dot), 1);
                    });

                    RAF(animate);
                }

        }
        },
        mounted(){
           this.animate();
        }
    }
</script>
